Yttria modified barium titanate capacitor



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YTTRIA MODIFIED BARIUM TITANATE CAPACITOR y Filed Jan. 3, 1966 W3 m//////)////////////////l a NQ QJ Il n Il y s. 8 X Ew QQ Q I PUZWOOUWQOQYQIJ 7had an average` Unite States U.S. Cl. 317--258 3 ClaimsABSTRACT OF THE DISCLOSURE A uniform dielectric constant ceramic of afired combination of barium titanate and about 7-12% yttriurn oxide.

This invention relates to ceramic barium titanate having an extremelyuniforrndielectric constant over a broad range of temperatures.

There is no standard ceramic dielectric; each 'one is speciallyformulated to suit a particular application. The present invention hasfor its primary object the formulation of a ceramic dielectric which hasits temperature coeicient of dielectric constant controlled within verynarrow limits.

FIGURE 1 is a plot of the percentage change in dielectric constant oftwo formulations within the scope of the present invention as comparedwith a third formulation.

FIGURE 2 is a side view in section of a ceramic capacitor employing thedielectric of the present invention.

The object of the present invention has been achieved by the addition offrom 7-12% of yttrium oxide (Y2O3) to barium titanate.

200 grains of commercial BaTiO3 powder and 2O grams of powdered yttriumoxide were sluriied with water and mixed in a porcelain ball mill w'ithporcelain balls. The mixture was milled for 8 hours and then pan driedin an oven. A paraffin binder was intimately mixed therewith. The blendwas forced through a 40 mesh screen and the material retained on a 100mesh screen was employed herein. This powder was pressed in a standardpill-making machine to form discs which would fire down to discs ofViti" diameter and about .020" thick. The dises were placed into anelectric furnace, the temperature raised to 2630 F. over a period of 5hours and held there for 1 hour to accomplish sintering of the discs.Silver electrodes were red on the opposing faces of 12 discs.

The ceramic capacitor discs of the above formulation dielectric constantof about 1000 over C. to +125 C. This value does not vary or -2% overthe temperature range sce cuiye A of FIGURE 1. The diswith a maximum ofthe range 55 more than +4.5% of 55 to +125 C., sipation factor is 1.0%at C., 1.6% at 55 C.

The ceramic capacitor discs of the above formulation have an averagedielectric constant of about 1045 at 25 C. At 55 C. this drops to avalue of only 990 and at 105 C. and 125 C. it drops to 980 and 1010respectively, see curve A of FIGURE 1.

Using the same procedure a second group of 12 capacitor discs wereformed having 7/2 yttrium oxide therein. As shown by curve B, theseunits have an average dielectric constant of about 1380 and 25 C. Thisvalue drops to only 1300 at -55 C. and at about 105 C. and 125 C. to1280 and 1330 respectively.

Patented Feb. 17, 1970 at 25 C. This value drops significantly to 1930at 55 i C. and to about 2270 and 2330 at C. and 125 C. respectively.

These examples illustrate clearly the efficacy of yttrium oxide inflattening the TC curve of a barium titanate ceramic when the yttriuinoxide is present within a range of about 7-120/0. At percentages lessthan this, the variation in dielectric constant over the range 55 C. toC. is considerable. Circuits containing capacitors employing thedielectric of curve C would have to be designed with far greatertolerances than circuits employing curve A or B type capacitors. Inother words, by the use of A or B type dielectrics, one significantvariable has been, for all practical purposes, eliminated.

FIGURE 2 illustrates a conventional ceramic capacitor 10 utilizing adisc 11 of ceramic dielectric of the present invention. On opposite sideof the disc lare silver electrodes 12 and 13.

While the present invention has been illustrated by means of modifying acommercial barium titanate (i.e. Ba'l'iO3) containing up to 2% alkaliand/or alkaline earth metal oxides) it is to be understood that purebarium titanate may also be modified. Furthermore, Abarium titanatecontaining conventional prior art additives designed to improve certaincharacteristics can also be employed herein. j

The foregoing examples are presented for purposes of illustration andare not intended to limit the instant invention. Various changes andmodifications, obvious to those skilled in the art may be made withoutdeparting from the scope of the invention.

What is claimed is:

1. A ceramic capacitor comprising a pair of electrodes separated by adielectric ceramic composition consisting essentially of a tiredcombination of barium titanate and from about 7-12% yttrium oxide.

2. The capacitor of claim 1 wherein said composition contains 71/2%yttrium oxide.

3. The capacitor of claim 1 wherein said composition contains 10%ytti'iurn oxide.

References Cited UNITED STATES PATENTS 2,616,813 11/1952 Klasens 106-392,735,024 2/1956 Kulcsar 106-46 X 2,985,700 5/1961 Johnston 106--39 XFOREIGN PATENTS 755,860 8/1956 GreatBritain.

OTHER REFERENCES Sauer, H. A. and Fisher, I. R.: Processing of PositiveTemperature Coefficient Thermistors, in Journ. Amer. Cer. Soc., 43,1960, pp. 297-301.

HELEN M. MCCARTHY, Primary Examiner W. R. SATTERFIELD, AssistantExaminer

